The present invention relates to system for remotely controlling access to motor vehicles, and more particularly to wireless remote control systems that can be used to unlock vehicle doors, start the engine and operate other functions on the vehicle.
Automobiles have used keys which mechanically operate locks to limit access to the vehicle and starting the engine to only authorized persons. More recently remote keyless entry (RKE) systems have been provided that use a small radio frequency (RF) transmitter, often having the shape of a key ring fob, to access the vehicle. This RF transmitter has a number of push button switches allowing the driver to control different functions of the vehicle, such as lock and unlock the doors, arm a security system or open the trunk. These transmitters also have been proposed to control starting the vehicle engine. When a given push button switch is operated, the transmitter sends an RF signal which carries a digital numerical code and a designation of the function to be performed. A receiver in the vehicle receives the transmitter signal, verifies that the numerical code designates an authorized transmitter for that particular vehicle and if so, signals the vehicle control circuits to perform the prescribed function.
Although the digital numerical code makes it extremely difficult for unauthorized persons to gain access to the motor vehicle, concern has been expressed that someone with a radio receiver and a digital signal analyzer could eavesdrop on the radio transmissions and obtain the security numbers. Particular brands of vehicles use a specific single radio frequency. Thus a thief could xe2x80x9cstake outxe2x80x9d a valuable vehicle to await the return of the driver and learn the transmission necessary to operate the vehicle. Those security numbers then could be utilized to steal that vehicle at a later point in time. Thus, as the technology available to thieves advances, so too must the signal processing employed by the RKE system. Therefore, there exists a need for a more secure radio frequency system that allows keyless entry.
Bidirectional radio frequency communication has been used for some time in cordless telephones. The term xe2x80x9ccordless telephonexe2x80x9d as used in the telecommunication industry, means a telephone comprising a base station and a hand-held transceiver unit. The base station is connected by wires to a terrestrial telephone line serving the owner""s premises. A hand-held transceiver carried by the user communicates by radio frequency signals with the single base station that is up to approximately 300 meters away.
The Digital Enhanced Cordless Telecommunications (DECT) protocol was developed in the mid-1980""s as a pan-European standard for cordless telephones and has been adapted for use outside the European Union. The DECT standard protocol has been used for simultaneous bidirectional communication between a base station and a hand-held transceiver of cordless telephones. This standard utilizes ten frequencies for communication. The exchange of signals over each frequency is divided into frames 10 each having twenty-four slots as shown in FIG. 1. The twelve slots in the first half 14 of each frame are used for communication from a hand-held transceiver to the associated base station, while the twelve slots in the second frame half 16 are used for communication from the base station and the hand-held transceiver.
When a user desires to use activates the cordless telephone to make an outgoing call, the hand-held transceiver searches for a frequency that has a matching slots in each frame half which are not being used by another cordless telephone system. This is accomplished by the hand-held transceiver listening for digital signals being sent in each slot of the frame at each of the assigned frequencies. When a vacant pair of slots, such as 18 and 19, is found, the hand-held transceiver sends a message initiation signal on the selected frequency during slot 18 in the first half of a message frame.
While the hand-held transceiver is performing these functions, the base station is scanning the ten frequencies and listening during each of the twelve slots in the first half 14 of the message frames at each frequency. When the base station hears a message initiation signal that is addressed to it, i.e. containing the proper identification data, the base station sends a response to the transceiver in the associated slot 19 in the second half of a frame at the same frequency and bidirectional communication is established. A reverse procedure occurs when the base station receives an incoming call via the terrestrial telephone line.
A general object of the present invention is to provide a remote keyless vehicle entry system which does not require manual activation by the user.
Another object is to provide secure mechanism for enabling a driver to start a motor vehicle without a conventional key.
A further aspect of the present invention is to provide a mechanism for automatically locking the doors upon the driver exiting the motor vehicle.
Still another aspect of the present system allows the vehicle doors and trunk to be unlocked and locked.
These and other objectives are satisfied by a passive keyless access system having a remote control adapted to be carried by the driver. Access to the vehicle is controlled by the remote control transmitting a signal from outside the vehicle to a control circuit on the vehicle. The control circuit measures the strength of the signal and activates a first function of the vehicle when the strength exceeds a first predefined threshold. Thereafter when the strength exceeds a second predefined threshold, the control circuit activates a second vehicle function. For example, the first function can be unlocking a vehicle door and the second function can be enabling the engine to be started. In that example, the first predefined threshold is greater than the second predefined threshold.
In the preferred embodiment of the present invention, transmission of the signals utilizes the Digital Enhanced Cordless Telecommunications (DECT) protocol. As an optional feature the control circuit can activate a third function of the vehicle when the signal strength drops below a third predefined threshold, the control circuit activates a second function of the vehicle, such as locking the doors as the driver has left the vehicle.